1. Field of the Invention
This application relates to semiconductor processing and, more particularly, to the selective oxidation of silicon relative to metal-containing materials, such as metal nitrides.
2. Description of the Related Art
Semiconductor device fabrication is a complex process. Devices are typically formed on a semiconductor substrate, and often include conductive elements separated by insulating elements. Conductive elements may serve as electrodes and interconnecting conductors, and may be formed from materials such as polysilicon or metal.
Various electronic devices, such as transistor devices, exist in the modern day fabrication of integrated circuits, with metal-oxide-semiconductor field-effect transistors (MOSFET) being a common transistor device. Generally, a MOSFET includes a conductive gate electrode formed over a gate dielectric, which in turn overlies a semiconductor substrate that is typically single-crystal silicon. For reliable MOSFET performance, it is important to maintain the conductivity of the gate electrode, which may be composed of conductive materials such as metal or metal nitride.
To achieve a MOSFET with desirable characteristics, oxidation is often performed on certain components in a semiconductor device, such as to form dielectrics. For example, silicon oxide can be created by oxidizing a silicon substrate. Unfortunately, conditions during the oxidation of silicon materials often result in oxidation of exposed metals. For example, performing oxidation of a silicon substrate while a metal or metal nitride structure is exposed can result in a layer of metal oxide forming around the metal or metal nitride. This metal oxide layer consumes the desired metal or metal nitride, reducing the conductive metal volume available for conducting current. As dimensions continually scale down, oxidation could effectively destroy the metal or metal nitride.
Since the metal or metal nitride may be readily oxidized to a point that its overall resistance is increased beyond useable levels, there is a need for selective oxidation. Selective oxidation employs methods that form the desired oxide components while at the same time minimize or preclude oxidation of, or oxide formation in, other components whose properties may be adversely affected by oxidation. Methods exist for selective oxidation that can effectively protect tungsten and molybdenum while oxidizing silicon. However, known selective oxidation techniques, such as use of dilute water vapor in H2 gas, while effective for preventing oxidation of tungsten, are ineffective at the protection of, e.g., titanium or titanium nitride.
Accordingly, there is a need for selective oxidation processes directed to maintaining the integrity of exposed metal-containing parts, such as titanium structures, while forming desired oxides in other exposed parts and preventing the nitridation of such desired oxides or reducing the nitridation of such desired oxides to acceptably low levels.